When dispensing carbonated beverages, particularly draught stout, it is desirable to obtain a close-knit creamy head. This contributes to a creamy taste and adds considerably to the customer appeal. Traditionally such heads are only obtained when dispensing such beverages from draught. Another factor that considerably enhances the appeal is the way in which, when dispensing from draught, small bubbles are intimately mixed with the body of the beverage as it is dispensed and then, after completion of dispensing they gradually separate out to form this close-knit creamy head.
The formation of such small bubbles liberated throughout the body of the beverage during dispensing can 5 be encouraged by causing shear of the liquid with resulting local pressure changes which causes release of small bubbles of controlled and uniform size. Over the years many proposals have been made to increase and control the generation of such heads on beverages. Our own earlier British Patent specification 1378692 describes the use of an ultrasonic transducer to subject the beer to shear immediately before it is dispensed into a drinking vessel and describes the way that by subjecting the initially dispensed portion of beer to ultrasonics the small bubbles released from this initial portion then gradually float up through the remainder of the beer forming nucleation sites and triggering the generation of further small bubbles of controlled size.
There have been many other proposals such as those described in GB-A-1280240, GB-A-1588624 and GB-A-2211854 to encourage the formation of the required close-knit creamy head on beers and other carbonated beverages. However, most of these proposals are concerned with formation of head as the beer is dispensed from draught.
GB-A-1266351 describes a system for producing a draught type head when dispensing beer, or other carbonated beverage, from a can or bottle. In the arrangement described in this specification, the container includes an inner secondary chamber which is charged with gas under pressure either as part of the filling process in which the container is filled with beverage or by pre-charging the secondary compartment with gas under pressure and sealing it with a soluble plug made from a material such as gelatine which, dissolves shortly after filling. The secondary chamber includes a small orifice and the overall arrangement is such that, upon opening the container and so reducing the pressure in the main body of the container, gas from the secondary chamber is jetted via the orifice into the beer in the main body of the container so causing shear and liberating the required small bubbles which in turn act as nucleation sites to trigger release of similar bubbles throughout the entire contents in the can or other container. The arrangements described in this patent specification are somewhat complex mainly requiring the use of a separate charging step after filling to pressurize the secondary chamber with the result that this technique has not been adopted commercially.
GB-A-2183592 describes a different technique which has recently achieved success in the market place. In this system the container of a beverage includes a separate hollow insert with an orifice in its side wall. As part of the container filling process beer is deliberately introduced into the inside of the hollow insert through the orifice and the pressures of the inside of the insert and the main body of the container are in equilibrium. Upon opening the container the beer is jetted out through the orifice into the body of the beer and again acts to shear liquid in the container with the result that a number of small bubbles are liberated which, in turn, act as nucleation sites to generate a number of small bubbles throughout the entire contents of the container. When dispensing a beverage from such a container into a drinking vessel the liberation of small bubbles throughout the entire volume of the beverage as it is dispensed gives a similar appearance to dispensing the same beverage from draught.
This system has many disadvantages. The use of such an insert occupies a substantial volume of the container and thus requires the use of a special, oversized container. Further, it is essential to remove all of the oxygen from inside the hollow insert before filling the container with beer. The presence of oxygen inside the container leads to the beverage being oxidised with a resulting impairment of flavour and risk of microbial growth leading to, for example, acetification of the resulting beverage when it contains alcohol. Thus, there is a general requirement to displace substantially all of the oxygen from a container, and its secondary chamber, when this is used, before the container is sealed. When the secondary chamber has the form of a hollow insert with only a small orifice in its wall and this insert is filled with air it is difficult to displace all of the air during the filling and sealing of such a container.
As a way of overcoming this problem GB-A-2183592 describes manufacturing such a secondary chamber by a blow moulding technique using an inert gas to form the secondary chamber and then only forming the orifice as the secondary chamber is placed into the container, for example by irradiation with a laser beam. However, in practice, this is not the way that such containers are filled. In practice, the secondary chamber is injection moulded in two halves one of which has a small orifice formed in its wall. The two halves are then welded together enclosing the normal atmospheric gases inside the secondary chamber. Such a secondary chamber is then inserted into an empty container and the whole is subjected to a reduced pressure, filled with a non-oxidising gas such as carbon dioxide, nitrogen, or a mixture of these, and evacuated again to flush substantially all of the oxygen from both the inside of the container and the inside of the secondary chamber before the container is again filled with a non-oxidising gas and then filled with beverage. In this way the amount of oxygen remaining in the sealed container is reduced to an acceptable level but these additional evacuation and flushing steps add a considerable delay and difficulty to the container filling stage with the result that the speed of filling is reduced to about 25 per cent of that in systems in which a secondary chamber is not included in the container. Also, since they require the use of a special, non-conventional filling machine this also imposes a considerable capital cost burden.